The present invention relates to a system and method for recycling multi-die packages containing faulty dies. The recycling of faulty multi-die memory package is accomplished by isolating the functional part of the package and using it as a smaller memory package.
Multi-die packages are well-known in the art of digital memory manufacturing. They are typically used when it is not practical to provide the required volume of memory with a single chip, due to die-manufacturing limitations.
As the dies used in multi-die packages are themselves large, their yield is finite and limited. Sometimes faulty dies are discovered in the “die sort” process, in which the dies are tested in the uncut wafer. However, some faulty dies are not detected until after the wafer is cut and the dies are assembled. At this stage, there is no way to make use of a functional die if one of the neighboring dies in the package is faulty. This causes a significant reduction in yield, and a significant loss of profit to the manufacturer.
By way of numerical example, if the probability of a die being discovered as faulty after assembly is 10%, then the probability of a faulty dual-die package is 19%, and the probability of a package with one functional die is 18%, resulting from the expression: 1−(0.9*0.9+0.1*0.1).
These percentages would result in affecting significant production quantities. A faulty multi-die package cannot be practically used as a single-die package, since it is not usually marked as faulty. In other words, the functional die is not singled out, and, in many cases, the presence of the faulty die disturbs the use of the functional die. It would be desirable to provide a method and means for using such faulty multi-die packages as single-die packages.
The problem described above is significant in situations where stacking of large dies is common. Typically, these cases arise mainly production of high-density flash memory devices (which are currently mostly NAND-type memory), and production of large DRAM devices. Stacking memory dies is a popular practice since this procedure provides greater density of dies for the same package area.
The cost of manufacturing large dies is high. In addition, large dies suffer from relatively high failure rates. While in other types of integrated digital circuits there is no way to make use of a portion of a component, memory chips are functionally homogeneous. Therefore, a portion of a memory device can, in principle, be useful as a smaller-capacity memory chip. There is no prior art describing a way to use memory chips that are partially damaged in production.
It would be desirable to have a method for recycling (i.e. converting) a faulty multi-die package into a package with a smaller number of active dies that can be practically used.